JPS605862A - Production of al-zn-mg alloy having excellent weldability and resistance to stress corrosion cracking - Google Patents

Abstract

PURPOSE:To obtain a titled Al-Zn-Mg alloy for which the ratio between the short diameter/long diameter and the length of the short diameter of the crystal grains after a final treatment are requlated by subjecting a casting ingot formed by reducing the crystal grain size of an Al alloy contg. respectively prescribed ratios of Zn and Mg, etc. to a homogenization treatment then to hot rolling at a specific reduction ratio or above. CONSTITUTION:An Al alloy contg., by weight, 3.0-8.0% Zn, 0.5-3.0% Mg, 0.005-0.20% Ti, 0.0005-0.05% B, 0.03-0.5% Cu and 0.5-1.0% Ag (exclusive of 0.5%) and contg. >=1 kind among 0.05-0.50% Mn, 0.05-0.40% Cr, 0.05-0.25% Zr, 0.01-0.15% V and 0.01-0.15% Mo is treated in the following way: The casting ingot formed by reducing the crystal grain size of the above-mentioned alloy to <=1,500mu is subjected to a homogenization treatment for 1-24hr at 400- 550 deg.C and thereafter the ingot is hot worked at >=60%, more particularly >=80% at 350-500 deg.C then the hot rolled alloy is subjected to soln. heat treatment and hardened. As a result, the intended Al-An-Mg alloy for which the ratio between the short diameter/long diameter of the crystal grains after the final heat treatment is >=1.5 and the length of the short diameter is <=80mu is obtd.

Description

[Detailed description of the invention] The present invention provides weldability and resistance to corrosion.
The manufacturing method of Zn-h transfer alloy is carried out using 1 equipment.

In general, AI Zn M bi-based alloys are
! Excellent J properties and weldability (Suruta, l/), Railway It
A very wide range of land structures, etc. in the area
One, many (important).

However, this kind of high strength A1 go'rt f soil, A'J
Therefore, the stress corrosion cracking force per shot is less than 1), and Al-Zn-Mg alloys are no exception. When increasing, 1
4・A and the stress corrosion resistance of the welded part rL resistance force ζ′I will occur.

t Still AlZn-Mg alloy (soil, l\1 alloy, the highest strength that can be welded 4 = J 11, barley)
As the Zn content increases, weldability also deteriorates.

This is the sound intensity welding groove i J11 small, l I)
1) The 11 shots are also the cause of the blockage b).

Therefore, stress) age corrosion cracking 1. 5) 1. Current 1. 1. Improvements in the contained ingredients and manufacturing conditions 1. Therefore, stress corrosion cracking occurs except in the thickness direction of m. There is a possibility that stress corrosion cracking may occur in the welded part (1) depending on the welded part (1) and the conditions of use.

In recent years, due to the increase in the size of structures and the rationalization of IIC measurement and construction, the use of thick materials has increased, and the stress generated in the welds is large, and the stress resistance of the welds is There is a strong demand for improved corrosion and cracking resistance.

The present invention aims to solve various problems associated with high-strength Al-Zn-Mg metal alloys as explained in section 1-2 above. The present invention provides a method for manufacturing an alloy.

The manufacturing method of the l\1-Zn tV1g alloy with excellent weldability and stress corrosion cracking resistance 1'J according to the present invention is as follows: Zn 3.0-8.0%, MBo , 5
~3. Ou+j%, 1゛i 0.005-0.20u+
L%, B O,0005-(1,05u+L%, CLI
(1,03~0.5u+1%,]\g0.5・~1.0
1% (excluding 0.5uuL%), and M
u O, 05-0, 50u+L%, CrO, 05-0,
40u+L%, Zr0105-0.25+u 1%, V
O, 01-0, 15u+t%, Mo 0.01-0.
An ingot containing at least one insert selected from 15u+1% and refined to a grain size of 1500 μV of A1 alloy consisting of residual aluminum and impurities was heated at a temperature of 400 to 550'C. After homogenization treatment between 1 and 241 Lν at a temperature of 350 and 500'C,
Hot cutting is carried out at a processing rate of 0% or more, and after Jυ final ripening heat treatment, the ratio of the short axis to the long axis of the crystal grains is 1:13 or more, and the length of the short axis is SOμ. The purpose is to do the following.

Weldability and stress corrosion cracking resistance layer according to the present invention1. The method for producing an AIZn-Mg alloy with excellent weldability improves stress corrosion cracking resistance without impairing weldability. They developed and applied for a manufacturing method for AI-Zn-Mg alloy, and as a result of subsequent research, they discovered the following.

In other words, stress corrosion cracking is a type of brittle fracture that occurs at grain boundaries, and the initial cause of its occurrence is said to be preferential elution of the grain boundaries due to the potential difference between the grain boundaries and within the grains, and the stress corrosion cracking process 1 Because it is caused by tensile stress, the stress applied to the grain boundaries, that is, the shape of the crystal grains, is greatly affected, and the weld area near the weld becomes a recrystallized structure due to the thermal effect during welding.
The stress distribution applied to the grain boundaries becomes larger compared to the elongated grain shaving material, and the stress corrosion resistance is 1i! The effect of "It cracking tendency" is gone, and from this reason, the resistance month II! l Corrosion resistance deteriorates.

Therefore, the inclusion of CLI, A =, has the effect of inhibiting the preferential elution of grain boundaries and improving the curve/1 stress corrosion cracking resistance. However, even if CLI or A8 is contained alone, the stress corrosion cracking resistance will be improved.The effect is 1:1, and if the content is increased, weldability and corrosion resistance will be deteriorated. Therefore, it is difficult to improve the stress corrosion resistance even if the content is increased. Therefore, CLI,A
By containing two types of B in appropriate amounts in the same ++j7,
The υ resistance to 7J corrosion and cracking can be significantly improved by a synergistic effect, not just an additive effect, without deteriorating the weldability.

In addition, in Al-Zn-Mg alloys, as the N-18 and Zn contents increase, the number of 417 particles at the grain boundaries increases and the melting temperature increases, so the temperature rise during welding and the shrinkage during solidification occur. If cracking at grain boundaries is likely to occur due to stress, or if the crystal grain size of the ingot is refined to 15 (10μ or less),
After uniform Tj treatment at a temperature of 0 to 550°C for 1 to 24 hours, hot working of 60% or more is performed at a temperature of 350 to 500'C to reduce the ratio of the short axis to the long axis of the crystal grains to 1: 5 or more, and the length of the short axis is 80μ or less)
8 It improves the stability.

Excellent weldability and stress corrosion cracking resistance A according to the present invention
Next, the method for manufacturing the I-Zn-h alloy will be explained.

First, the components and proportions of the AlZn-Mg alloy used will be explained.

Zn is the most important element for improving strength, and the content is 3. If Ou+1% is less than 1-ei, the optical intensity cannot be increased to 1S, and if the content exceeds 8.0%, stress corrosion cracking is likely to occur. Therefore, Zn
The fi quantity is 3.0=8.0+u1%.

Like Zn, Mg is an important element for improving strength, and if the content is less than 0.5wL%, it will not have sufficient strength, and if the content is more than 3.0LllL%, it will increase the stress.
91. Eclipses are more likely to occur. Therefore, Mε
The content is 0.5 to 1. [)+111%.

1'1.13 is an important element for the formation of the group j & micro 4111 of the daj mass, and the i' i content is 0.005u+1
%not+i:l! Contains i and 13"i Ka0. (10
05tu less than 1% f 1. t M Grain 1'fA 1
lll conversion 1. :: No effect 1. T, T i 0
．． 20+uL%t; , k Hi13 (1,05+uL
If the content exceeds 1%, there is a possibility that giant compounds will occur. , 1 means ``1-containing triha 0.005-0
．． 20wL%13, J: HiB content 0.0005
-1), 05+u1% tossle.

CLI and A8 improve stress corrosion cracking resistance by simultaneously containing 2Jffi, but
Contained Q CLl (1,0311% unil:ej,
A (HO, 5u + 1% non-h:tj r li does not have such an effect even if it is added at the same time, and Cu
O, 5% I%, At; 1. If 1% of Ou] is contained, the effect will be saturated, and the effect will be saturated. i91 is more likely to occur. Yotte, Cu content 1j: 0.0:I −
0.5u+t%, AB content is 0.5-1.01% ((
1.5+IIL% is not included).

1. Cr, Zr, ＼, ′, MO are necessary elements for stabilizing the structure, and whether the crystal grains are finely controlled by a combination of homogenization and hot working, or whether they are included? , is M++0.05
u + L% unknown J, Cr 0.05 + uL% unknown 111, Zr O, (15u + 1% unknown γ; ei, \I 09
01u+I%un7:I:i, to 4o fl, o1u+L
In
O, 5() 1%, Cr・0.40u+L%, Zr O
,25u+1%,\' 0. ]5u+1%, MoO,
] If the content exceeds 5u+1%, there is a possibility that a giant compound will be generated. Therefore, the river containing Kiri 11 is 0.
05-0.5lll%, Cr content is 0.050.40
u+1%, Zr containing enemies 0.05-0.25u+L%
, \' 0.0], -0, ]5u+L%, Mo 0.0
] ~0.15u+L%.

Note that the impurities mainly include Fe and Si as unavoidable impurities.

Such content components and component ratios\I-χ11-
The crystal grain size of the ′+)j lump formed by melting Mg alloy is 1
゛1. Due to the inclusion of B, the crystal grain size is refined to 1500μ or less, and if the grain size is heated above 1500μ, the grain size of the product will increase and the weldability will deteriorate, so the grain size of the J lump should be Must be 1500μ or less.

Next, heat treatment will be explained.

2) J mass at 4 (10-550'C) temperature 1-
Homogenization treatment is carried out for 24 hours at 400'C.
At temperatures below 84n, Cr, Zr, \・', Mo
The crystal grains of the product become enlarged due to insufficient precipitation of Cr.
Precipitates of V and Mo begin to form a solid solution again, and even if the crystal grains of the ingot are fine, the crystal grain size of the product increases and weldability deteriorates.

After this homogeneity ratio treatment, hot cutting of 60% or more (￥! or 8n% or more) is performed at a temperature of 5o-500'C (preferably 4oO-450oC) [post-solution treatment and quenching] Therefore, to4n, Cr, Z, r, \I', 1Vl
The compound o and l\1 inhibits the growth of recrystallized grains l! It stops and becomes a fine fiber structure, and as a result, the ratio of the short axis to the long axis is set to 1:5 or more, and the length of the short axis is controlled to 80μ or less.

[Thermal opening during hot rolling, hot extrusion, hot forging, etc.]
Second, it is difficult to process at temperatures as low as 350'C.5!11
, and at a high temperature of 1 degree exceeding 500 degrees Celsius, the temperature is 11 degrees.
There is a possibility of old 17Q warping, which increases the crystal grain size of the product and deteriorates weldability. In addition, if the processing rate is less than 60%, the crystal grain size of the product will increase, and if the ratio of the short axis to the long axis of the final product is less than 1 to 5 or the short axis exceeds 80 μ, welding will occur. Become less sexually active.

Excellent weldability and stress corrosion cracking resistance A according to the present invention
Examples of the method for manufacturing l-Zn-Mg alloy will be described together with comparative examples.

Example Al-Zn-M with the components and component ratios shown in Table 1
A dummy ingot prepared by SJJ using g-alloy by a conventional method was treated under the following conditions.

(1) Conditions for the production method of AI Zn M8 alloy with excellent weldability and stress corrosion cracking resistance according to the present invention After homogenization treatment at a temperature of 450°C for 24 hours, 90% After hot rolling, a 25m+nL plate 4.
I made 1.

(2) Comparative conditions After 24 hours of homogenization at a temperature of 570°C, 450-5
25m by 90% hot rolling at 00'C temperature.
A +nL plate was produced.

After performing solution treatment for 30 minutes at a temperature of 450'C, these plates were cooled with water and aged for 2.1 hours at a temperature of +20'C.

Table 2 shows the results of investigating the properties of this root 4.].

1) Particles of 111 pieces of ice: A cross section parallel to the hair direction of the plates and shapes A and A.

2) 11il Otl 'C
/lNaCl,'((i3/1KHcrr(
L, -: NIH; /l (2r Ol: iA combined water lf: n (8-ko immersion) [did. OG: no cracking at 0 minutes, Xα: 0
111 leaks occurred in minutes.

:() Swant type 1'tire test: Thickness] 2 mml
A 7-slit type weld crack test piece was used.

Crack % = Crack length / All welding members

Thickness G inn L Weld filler 4'A'! 'i: 856 Electrical Iit 26+1 ＼ Voltage 3oV Table 2 shows the welded area of J3 in Copper O-no Tsuki 911 corrosion resistance: 4) Using the butt welded part of the same specimen, as shown in the accompanying drawing τj. A stress of 15 KPi/nun2 was applied to the support fitting 3 having the pin 5 by a three-point support method to support the temporary phase 1 with the weld bead 2.

Test conditions] (3g of 10”C/1Nacl 368/I(
,:t・0, -30 g/l K2Cr20
No. 7 was submerged in a mixed aqueous solution and cracks were observed.

As is clear from Table 2, the temporary phase manufactured under the conditions of the manufacturing method according to the present invention has superior weldability compared to the plate materials manufactured using comparative flexibility, and is also resistant to lunar eclipse cracking. I can see that you are in love with sex.

[Brief explanation of the drawing]

Appendix 4 = I drawing shows the test method for stress corrosion cracking resistance of welded parts 41! X is a schematic diagram. 1 to plate 4, l, 2 to weld bead', (to/support metal fitting 1, 1 to crack occurrence area, 5 to pin.

Claims (1)

[Claims] Zu 3.0-8,0+uL%, M60.5-3,0w
t%, T i O, 005-0,2 (buL%, B 0
00005-0.05wt%, CuO,03-0,5
wL%, AgO,5-1,O+u1% (0,5u+L%
), and Mu O,05-0.50
1%, CrO, 05-0, 40uL%, χrO,
05-(1,25u+t%, V 0.01-0.15w
L%, Mo O, 01-0, 15u+L%, including at least one insert selected from among L%, Mo O, 01-0, 15u+L%, the crystal grain size of A1 alloy consisting of a small amount of Al and impurities was made fine to 1500 A or less +l:+11 After homogenizing the ingot at a temperature of 400-550°C for 1-24 hours,
Processing of 60% or more at a temperature of ~500' 80 μ or less for weldability; and stress corrosion resistance and cracking resistance).